There is growing evidence that cell deformability (i.e., the degree to which a cell changes shape under an applied load) is a useful indicator of abnormal cytoskeletal changes and may provide a label-free biomarker for determining cell states or properties such as metastatic potential, cell cycle stage, degree of differentiation, and leukocyte activation. Clinically, a measure of metastatic potential could guide treatment decisions, or a measure of degree of differentiation could prevent transplantation of undifferentiated, tumorigenic stem cells in regenerative therapies. For drug discovery and personalized medicine, a simple measure of cytoskeletal integrity could allow screening for cytoskeletal-acting drugs or evaluation of cytoskeletal drug resistance in biopsied samples. Currently, these applications often require costly dyes, antibodies, and other reagents, along with skilled technicians to prepare samples. A simple label-free deformability measurement in which cells are minimally handled has the potential to greatly reduce costs and allow routine cell screening and classification in clinical and research applications.
Current platforms and techniques that measure cell deformability have suffered from a number of limitations. These include low throughput as well as inconsistent results. As a result, these technologies have not had any significant clinical impact. A wide variety of platforms have been engineered to perform mechanical measurements on cells. Generally, these techniques can be divided into two categories based on the samples they act on: bulk and single-cell. Bulk platforms, such as microfiltration, tend to have high throughput, but they yield one endpoint measurement and do not take into account heterogeneity within the sample population of cells. Disease may develop from abnormalities in a single cell thus accurately detecting rare events or local variations is important and bulk measurement of these types of samples may result in misleading averages. Single-cell platforms that can assay this heterogeneity include micropipette aspiration, atomic force microscopy (AFM), magnetic bead-based rheology, microfluidic optical stretching, and biophysical flow cytometry.
However, these approaches are typically optimized for biophysics research and operate at low rates at around 1 cell/minute for AFM and optical stretching. Applications in clinical diagnostics or drug screening will necessarily require large sample sizes to obtain statistically significant results. This cannot reasonably be achieved using low throughputs on the order of 1 cell/minute. Further, these techniques also suffer from other disadvantages. AFM, for example, requires a skilled operator and measurements are slow. Rheological techniques can yield drastically different mechanical properties that are difficult to standardize even amongst a single cell type. In addition, these techniques require microscopic observation at high magnification for a period of time such that the overall throughput is very low (<<1 cell/minute). The manual, low-throughput nature of current methods that measure cell mechanical properties has limited the capability for development of practical biomechanical biomarkers for translational use, as well as limited the progress of understanding molecular components underlying cell mechanical properties.